In the auditory system, striking transformations in the representations of stimuli occur between the auditory midbrain (inferior colliculus) and the auditory cortex. In all species, the single tonotopic representation in the central nucleus of the inferior colliculus (ICc) gives way to multiple tonotopic areas in the primary auditory cortex and these multiple cortical areas exhibit segregation of function. Because the transformations between the ICc and auditory cortex are fundamental, it is important to know where and how they occur. The proposed studies address 1) the anatomical projections from distinct parts of the central nucleus of the ICc to the tonotopic parts ('core areas) of the medial geniculate (MG), and the projections from core areas of the MG to the auditory cortex and 2) evaluation of whether different pathways carry different information. An understanding of the organization of the multiple parallel pathways making up the ascending auditory system is a fundamental component for understanding the mechanisms of auditory function. This knowledge is expected to provide information that can be used in making rational choices of potential targets for direct brain stimulation in deaf patients who cannot use a cochlear prosthesis or in intractable disorders such as tinnitus. PUBLIC HEALTH RELEVANCE: Understanding the transformations that occur in auditory representations in the forebrain auditory pathways will be important for designs of speech processors for cochlear implant users, selecting targets for direct brain stimulation in deaf patients who cannot use a cochlear prosthesis, and in intractable disorders such as tinnitus.